The present invention relates generally to a suspension mechanism, particularly to a suspension mechanism for an objective lens of an optical head accommodated within an optical disk driver.
During operation, an objective lens of an optical head must be operated to track the tracks of an optical disk and focus laser beams on the optical disk to facilitate reading information from the optical disk or writing information into the optical disk. However, to track the tracks of an optical disk, the objective lens must be driven to swing back and forth on a plane parallel to the surface of the optical disk. Similarly, to focus laser beams on an optical disk, the objective lens must be driven to approach or move away from the optical disk.
The conventional mechanism for tracking the tracks of an optical disk or focusing laser beams on an optical disk is shown in FIGS. 1 and 2. An objective lens 10 mounted on an objective lens seat 11 is suspended on a rotation beam 13 by means of four thin parallel leaf springs 12. A shaft 14 is mounted on the central portion of the rotation beam 13, and a lower bearing 15b for rotatably supporting the shaft 14 is mounted on a base 16. Furthermore, an upper bearing 15a is mounted on the upper portion of the shaft 14 to cooperate with the lower bearing 15b to rotatably support the shaft 14. The upper bearing 15a is urged downward by one end portion of a leaf spring 18, while the other end portion of the leaf spring 18 is secured to the top portion of the "L" shaped base 16 by means of a plate 17. With this arrangement, the shaft 14 can be held upright. Also, two pairs of coils 19a and 19b, orthogonal to each other, are secured to the four sides of the objective lens seat 11. When electric currents pass through the coils 19a or 19b, the magnetic forces produced between the coils 19a, 19b and permanent magnets (not shown) fixed on the base 16 will drive the objective lens seat 11 together with the objective lens 10 to swing around the shaft 14, that is, to move in the direction of the arrow AA' to facilitate a tracking operation of the objective lens 10, or to move up and down to facilitate a focusing operation of the objective lens 10.
In the above-described mechanism, the tracking operation of the objective lens -0 is accomplished by rotational movements of the rotation beam 13, that is, rotational movements of the shaft 14 relative to the base 13. However, the shaft -4 is supported by the bearings 15a, 15b, and frictional forces induced at the beginning of rotation movements of the bearings 15a, 15b will greatly reduce the responsiveness of the whole mechanism. Furthermore, the precise positioning of the objective lens 10 will be affected, because of the friction of the bearings 15a, 15b. Also, the roughness of the surfaces of the rollers and the raceway of the bearings will inevitably induce noises into output signals of the whole system.